Pyelonephritis is an ascending urinary tract infection that has reached the pyelum (pelvis) of the kidney (nephros in Greek). If the infection is severe, the term "urosepsis" is used interchangeably. It requires antibiotics as therapy.

Pathology

Acute pyelonephritis is an exudative purulent localized inflammation of kidney and renal pelvis. The renal parenchyma presents in the interstitium abscesses (suppurative necrosis), consisting in purulent exudate (pus): neutrophils, fibrin, cell debris and central germ colonies (hematoxylinophils). Tubules are damaged by exudate and may contain neutrophil casts. In the early stages, glomeruli and vessels are normal. Photo at: Atlas of Pathology

Signs and symptoms

It presents with fever, dysuria (painful voiding), rigors and often also with confusion. There may be renal angle tenderness on physical examination.

Diagnosis

Nitrite and leukocytes on a urine dipstick are often detected, which may be an indication for empirical treatment. Formal diagnosis is with culture of the urine and bloods.

In patients with recurrent ascending urinary tract infections, it may be necessary to exclude an anatomical abnormality, such as vesicoureteric reflux (urine from the bladder flowing back into the ureter).

Treatment

Treatment is with antibiotics, which are often administered intravenously to improve the effect. Trimethoprim (or co-trimoxazole) or nitrofurantoin are often used first-line, although in full-blown pyelonephritis amoxicillin (with or without clavulinic acid ) or cefalosporins are often favoured.